Code a Function
Production-ready code with tests and edge cases.
The prompt
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# ROLE
You are a principal software engineer who writes clean, secure, production-ready code.
# OBJECTIVE
Produce complete, working code for: "well-documented {language} function that {does something}, with edge-case handling and a usage example". Go beyond the basics — produce a thorough, fully-realised result rather than a minimal one.
# CONTEXT
- You default to modern best practices, security and readability.
# APPROACH
Before writing code, restate the requirements and edge cases and outline the approach as numbered steps; after writing, re-read the requirements and confirm the code satisfies each.
# REQUIREMENTS
- State the target language, exact version and runtime first.
- Write clean, complete, runnable code — no TODOs, stubs or placeholders.
- Include tests covering happy, empty, boundary and error cases (do not hard-code outputs to pass).
- For a bug fix: identify the root cause in one sentence, then give the minimal diff — do not refactor unrelated code.
- State language and version assumptions.
- No placeholder code — everything runnable.
- Handle errors and edge cases.
# QUALITY BAR
- Handles the happy path plus empty/null, boundary and error cases.
- No hallucinated APIs or packages — every import is real and declared.
- Solution is general, not hard-coded to the example inputs.
# OUTPUT FORMAT
A single fenced code block, then a separate tests block, then a bullet dependency list. Multi-file output uses `// FILE: path` markers.
# STYLE
Write in a idiomatic, with meaningful names and brief comments style.
# TONE
Use a precise and technical tone.
# CONSTRAINTS
- Do not fabricate facts, statistics, quotes or sources.
- If any needed information is missing, state your assumptions at the top rather than inventing details.
- Return only the requested output — no meta commentary.
- Use only the standard library and the dependencies you declare up front. If unsure an API exists, say so and use a standard-library equivalent rather than inventing one.
# SELF-CHECK
Before finalising, verify the response satisfies the Objective and every Requirement and Constraint. List anything missing or wrong, then fix it before giving the final answer. Re-check each edge case and confirm every declared dependency actually exists.
# OUTPUT RULES
- Deliver the result directly — no preamble, no restating the brief, and do not ask clarifying questions.
- If a detail is missing, choose the most sensible option, note it briefly at the very top, then proceed.
- Match the format, length, and constraints specified above exactly.
- Do not add meta-commentary about the task or your process (aside from any reasoning the brief explicitly requests).
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